1. Field of the Invention
This invention relates to a femur prosthetic device. More particularly, this invention relates to a hip prosthesis adapted for insertion into the upper medullary canal in the femur of a patient. The hip prosthesis of this invention is of the type generally characterized as including a head or ball member, a shaft or stem member for insertion into the intermedullary canal, and a neck member connecting the head and stem, and also including at least one porous metal surface portion which provides for stabilization by bone ingrowth without requiring any cement.
2. Description of the Prior Art
Hip prostheses are known in the art and these have included various design configurations of the various components, including the head member, neck, collar and stem. Several of these prosthetic devices have been provided with porous surfaces for bone ingrowth. Representative of patents in this field include U.S. Pat. No. 3,906,440 to W. Rostoker and J. Galante, British Patent Specification 1,554,454 to J. C. Bokros, and European Patent No. EPO 038,902 A3 to Gebruder Sulzer Aktiengeseellschaft (Sulzer).
Nevertheless, further improvements in the total design of hip prostheses are required to assure stable fixation of the implanted prosthesis at the bone/metal interface. Thus, in cemented prosthetic devices, there has not been satisfactory fixation due to the various stress loads, i.e. the compression, shear and torsion to which the implanted device is subjected. These mechanical forces, especially shear and torsion, weaken the bone cement bond. In addition, it is known that there is a tendency for bone resorption which also weakens the cement bond between the bone, e.g. intramedullary canal of the femur and the femoral prosthesis.
On the other hand, by providing a bond ingrowth surface on the prosthetic device, a more stable fixation would be expected and some advances along these lines have been made. However, even with prosthetic devices provided with a bone ingrowth surface or surfaces, sufficient bone ingrowth to provide long term stabilization requires the prosthesis to be stably fixed without movement for at least 6 weeks, and any relative motion of the prosthesis during that period prevents or minimizes bony ingrowth. This is a particularly significant problem in view of the difficulty in fitting the prosthesis with sufficiently close tolerances to provide large contact areas between the porous material and the bone, even where the entire outer surface of the prosthesis is fabricated from porous material.
As a result, an incidence of 10 to 20% of femoral stem loosening or failure in total hip arthoplasty patients followed over 5 or more years, especially in younger patients, has been reported.